As is well known, polyolefins represented by polyethylene and polypropylene have various excellent physical, chemical, and mechanical properties and good moldability. Due to these advantages and because of their inexpensiveness, polyolefins are being extensively used in a wide range of industrial fields. However, since such polyolefins are nonpolar, they involve such a defect that it is difficult to make composite materials with polar materials such as metals, glass, and polar high-molecular weight materials. As an expedient for overcoming this defect, copolymerization of olefin polymers with monomers having a polar group is widely known. However, it is hard to say that such copolymers have sufficient adhesion and, in addition, their heat resistance is insufficient. Under these circumstances, it has been proposed in JP-W-63-500179 to blend these copolymers with polyolefins. (The term "JP-W" as used herein means an "unexamined published international patent application".) Further, JP-A-60-63240 proposes to blend those copolymers with elastomers. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".) However, these proposed compositions do not always show sufficient adhesive strength. Although blending with a large proportion of an elastomer brings about a slight improvement in adhesive strength, such a composition not only has poor mechanical strength and but also, when molded into a film, shows poor anti-blocking properties and reduced solvent resistance.
JP-A-62-263241 proposes a composition comprising an ethylene copolymer containing a polar group, polypropylene, and an olefin copolymer rubber.
The above composition, however, has been found to have still insufficient adhesion to polar materials such as polar high-molecular weight materials.
The present inventors have conducted extensive studies on resin compositions obtained by melt kneading an ethylene copolymer containing maleic anhydride with a crystalline polyethylene resin, with respect to the kind, proportion, etc. of the blended resin. As a result, it has been found that the presence of both a high-rigidity component and a low-rigidity component is requisite for the development of sufficient adhesive strength and that there is an optimum rigidity value which an adhesive resin composition should have for attaining sufficient adhesive strength. It is known that the larger the energy absorbed during peeling, the higher the adhesive strength. This energy can be expressed by the product of the stress applied to the peeling site and deformation. If an adhesive resin composition has too low rigidity, the applied stress is small, while if it has too high rigidity, little deformation occurs. Thus, it has been ascertained through extensive investigations that optimum rigidity is present. The necessity of both of a high-rigidity component and a low-rigidity component has been proven by the fact that the presence of both components in an adhesive resin composition changes the deformation mode for the composition from elastic deformation to plastic deformation and, accordingly, serves to increase the consumed amount of peeling energy and make the composition less apt to be peeled off.
It has, therefore, been found that an adhesive resin composition having excellent adhesion can be obtained by adding a crystalline polyethylene resin as a high-rigidity component and a non-crystalline or low crystalline olefin copolymer rubber as a low-rigidity component, in specific proportions, to an ethylene copolymer containing maleic anhydride, and melt kneading these components. The present invention has been completed based on these findings.